#include<stdio.h>
int Fib(int n)
{
  int sum = 0,n1 = 1,n2 = 1;
  if(n<=2) return 1;
  int i = 0;
  for(i = 3;i<=n;i++)
  {
    sum = n1 + n2;
    int tmp = n1;
    n1 = sum;
    n2 = tmp;
  }

  return sum;
}


int main()
{
  int n = 0;
  scanf("%d",&n);
  
  int ret = Fib(n);

  printf("第n为的斐波那契值：%d\n",ret);

  return 0;
}
